U.S. Pat. No. 6,361,173 describes a projection system in which selective pixels in a projected image are inhibited so as not to project onto a subject (presenter) when the presenter walks in front of the projection screen. A preferred means for locating those image pixels projecting onto the presenter is the use of an infrared camera combined with infrared lamps to flood the screen with infrared illumination. The difference of the infrared reflection, between the presenter and screen, identifies those pixels in the presenter area.
Inhibiting the projected image from illuminating the presenter, permits the presenter to look toward his audience without being blinded by the projector. The prevention of the image from being projected onto the presenter's body also eliminates the distortion of that portion of the image, which is so disturbing to an audience.
Selective inhibition greatly aids the comfort and freedom of motion of the presenter. The presenter already blocks a portion of the screen image from view, while a second area is being blocked for many viewers by his shadow.